This invention relates to a method and apparatus for ON-LINE recognizing handwritten patterns and, particularly, to a method and apparatus for ON-LINE recognizing handwritten patterns which are liable to variation and rotation.
A conventional handwritten pattern recognition system operates in such a way that each handwritten stroke is divided into numerous short vectors and it is tested whether part or all of the vectors match the majority of vectors of a candidate pattern in the dictionary, as described in an article entitled "Application of DP Matching Process to Character Recognition", Nikkei Electronics, pp. 198-199, Nov. 7, 1983. This method is capable of character recognition even if the dimension of the input vectors differs from that of the dictionary vectors and is advantageous in recognizing correct-attitude handwritten patterns. However, because of the comparison process based on the direction of each vector, when a rotated character is entered, which results in a change in the direction of each vector, it becomes difficult to recognize the character, and therefore the method could not readily be applied directly to pattern recognition where the rotation of pattern occurs frequenctly.
There has been proposed another handwritten pattern recognition system operating in such a way that a handwritten pattern is decomposed into a plurality of segments, comparison is carried out between angular variations of adjoining segments and the counterpart of a candidate pattern stored in the dictionary to evaluate the difference between them, and the entered handwritten pattern is recognized depending on the degree of difference as disclosed in U.S. patent application Ser. No. 686,001 now U.S. Pat. No. 4,653,107. However, this method is entirely based on the comparison of the angular variations of adjoining segments between an input handwritten pattern and candidate patterns in the dictionary, and therefore it cannot deal with input handwritten patterns which are rich in variation. Namely, in FIG. 1a, an input handwritten pattern is approximated to segments a1, a2 and b, and adjoining segment pairs a1-a2 and a2-b have angular variations .DELTA..theta.1 and .DELTA..theta.2, respectively. In the recognition process, the input handwritten pattern of FIG. 1a, which is pertinent to a dictionary pattern shown in FIG. 1b, the angular variation .DELTA..theta.1 between the adjoining segments a1 and a2 of FIG. 1a is compared with the angular variation .theta. between the adjoining segments a' and b' in FIG. 1b, resulting occasionally in a judgement of inconsistency. The presence of the segment a2 in FIG. 1a is a result of a significant variation in the input handwritten pattern, and for a reasonable pattern recognition process, the angular variation across the three consecutive segments a1, a2 and b (i.e., .DELTA..theta.1+.DELTA..theta.2) should be compared with the angular variation between the adjoining segments a' and b' of the dictionary pattern shown in FIG. 1b.